A binocular holographic near-eye 3D display system based on liquid crystal polarization grating

Abstract

This invention proposes a binocular holographic near-eye 3D display system based on a liquid crystal polarization grating. The system includes a laser, a beam expander, a collimating lens, a semi-transparent mirror I, a spatial light modulator, a 4f filter system, a semi-transparent mirror II, a polarizer, and a liquid crystal polarization grating. The laser beam emitted from the laser is expanded by the beam expander and collimated by the collimating lens, then transmitted through the semi-transparent mirror I to the spatial light modulator. A hologram of a pre-generated 3D object is loaded onto the spatial light modulator. After diffraction by the spatial light modulator, the beam enters the 4f filter system, eliminating zero-order and stray light. The beam of light, after eliminating zero-order light and stray light, is modulated into linearly polarized light after passing through a polarizer. The linearly polarized light is reflected by a semi-transparent mirror II and then incident perpendicularly on a liquid crystal polarization grating. The left-handed and right-handed circularly polarized light contained in the linearly polarized light are deflected in opposite directions along the optical axis after passing through the liquid crystal polarization grating, thereby generating 3D reconstructed images with the same deflection angle in the left and right viewing areas, respectively, realizing binocular holographic near-eye 3D display.

Description

I. Technical Field

[0001] This invention relates to holographic display technology, and more specifically, to a binocular holographic near-eye 3D display system based on a liquid crystal polarization grating. II. Background Technology

[0002] Holographic 3D display technology, based on the principles of interference and diffraction, records and reconstructs 3D objects, completely preserving the wavefront information of the objects and achieving realistic display effects. It is considered one of the most ideal 3D display technologies. Holographic near-eye 3D display technology can suppress the convergence-accommodation conflict of traditional 3D near-eye display technologies, showing great potential in near-eye 3D display. Researchers at Microsoft Research Cambridge University proposed a monocular near-eye display based on phase-type holograms, integrating wide field of view and multi-focal functionality into the display device. However, this near-eye display only supports monocular viewing, lacking binocular display content. To achieve binocular holographic near-eye display, researchers at China Jiliang University reconstructed holograms of a 3D scene in the left and right viewing areas by loading them onto two spatial light modulators, achieving binocular holographic near-eye display with accurate depth information. Researchers at Beijing Institute of Technology built a binocular holographic near-eye display system using time-division multiplexing and a liquid crystal shutter device. Although this system only uses one spatial light modulator, it adds other optical components such as mirrors. Currently, binocular holographic display systems built using two spatial light modulators or additional optical elements are structurally complex and struggle to meet the requirements of lightweight and integrated near-eye displays. Therefore, designing a compact binocular holographic near-eye 3D display system is an urgent problem to be solved. III. Summary of the Invention

[0003] This invention proposes a binocular holographic near-eye 3D display system based on a liquid crystal polarization grating. (See attached diagram) Figure 1As shown, the system comprises a laser, a beam expander, a collimating lens, a half-mirror I, a spatial light modulator, a 4f filtering system, a half-mirror II, a polarizer and a liquid crystal polarization grating. The 4f filtering system comprises a lens I, a filter and a lens II. The laser emitted laser passes through the beam expander and the collimating lens, and then is transmitted to the spatial light modulator through the half-mirror I. The spatial light modulator is loaded with the hologram of the 3D object generated by the computer in advance. After the light beam passes through the diffraction of the spatial light modulator, it enters the 4f filtering system, so that the zero-order light and stray light are eliminated. After the light beam whose zero-order light and stray light are eliminated passes through the polarizer, it is modulated into linearly polarized light. After the linearly polarized light is reflected by the half-mirror II, it is perpendicularly incident on the liquid crystal polarization grating. The left-handed circularly polarized light and the right-handed circularly polarized light contained in the linearly polarized light are deflected in opposite directions along the optical axis after passing through the liquid crystal polarization grating, so as to generate 3D reconstructed images with the same deflection angle in the left and right viewing zones, respectively. The diffraction position of the holographic reconstructed image is set to be the same as the position of the camera, and the moving camera is used to simulate the two eyes to record the reconstructed images in the left and right viewing zones, respectively, so as to obtain the binocular holographic near-eye 3D display effect.

[0004] The liquid crystal polarization grating in the system has dielectric anisotropy and high diffraction efficiency. The liquid crystal polarization grating is based on geometric phase control, and its working principle is shown in the accompanying drawings. Figure 2 As shown, the laser is incident on the liquid crystal polarization grating to generate only two diffraction orders, i.e. +1 order and -1 order. The liquid crystal polarization grating selectively emits +1 order or -1 order diffracted light according to the polarization state of the incident light. When the laser irradiates the liquid crystal polarization grating, due to geometric phase control, the +1 order and -1 order diffracted light deviates from the original incident direction. When the linearly polarized light is perpendicularly incident on the liquid crystal polarization grating, the diffraction angle a of the +1 order and -1 order diffracted light satisfies the following formula:

[0005]

[0006] wherein Λ and λ g are the period and working wavelength of the liquid crystal polarization grating, respectively. As shown in Figure 2 (a), when the left-handed circularly polarized light is perpendicularly incident on the liquid crystal polarization grating, the polarization state of the diffracted light is modulated into right-handed circularly polarized light, and deviates from the optical axis by an angle a. As shown in Figure 2 (b), when the right-handed circularly polarized light is perpendicularly incident on the liquid crystal polarization grating, the polarization state of the diffracted light is modulated into left-handed circularly polarized light, and deviates from the optical axis by an angle -a. Since the linearly polarized light is regarded as a collection of left-handed circularly polarized light and right-handed circularly polarized light, as shown in Figure 2 (c), when the linearly polarized light is perpendicularly incident on the liquid crystal polarization grating, the polarization states of the left-handed circularly polarized light and the right-handed circularly polarized light in the linearly polarized light are changed, respectively, so as to form +1 order and -1 order diffracted light, respectively, and are deflected to the left and right viewing zones by angles a and -a, respectively.

[0007] Binocular holographic near-eye 3D displays require the reconstructed images to enter the viewer's left and right eyes respectively. Therefore, the distance between the two reconstructed images in the left and right visual zones needs to correspond to the interpupillary distance. The diffraction angle α and the interpupillary distance d satisfy the following formula:

[0008]

[0009] Where l represents the distance between the liquid crystal polarization grating and the human eye. This invention calculates the diffraction angle based on the distance between the liquid crystal polarization grating and the human eye, and the interpupillary distance, thereby determining the period of the liquid crystal polarization grating to meet the needs of binocular holographic near-eye 3D display viewing. IV. Description of the attached drawings

[0010] Appendix Figure 1 This is a schematic diagram of the structure of a binocular holographic near-eye 3D display system based on a liquid crystal polarization grating according to the present invention.

[0011] Appendix Figure 2 This is a schematic diagram illustrating the working principle of the liquid crystal polarization grating of the present invention, wherein... Figure 2 (a) shows the modulation when the perpendicularly incident light is left-handed circularly polarized. Figure 2 (b) shows the modulation when the perpendicularly incident light is right-handed circularly polarized. Figure 2 (c) shows the modulation when the perpendicularly incident light is linearly polarized.

[0012] Appendix Figure 3 This is a schematic diagram illustrating the reconstruction effect of a binocular holographic near-eye 3D display system based on a liquid crystal polarization grating according to the present invention. Figure 3 (a) is a 3D reconstructed image taken in the right view area when the reconstruction distance is 25cm. Figure 3 (b) is a 3D reconstructed image taken in the right view area when the reconstruction distance is 22cm. Figure 3 (c) is a 3D reconstructed image taken in the left view area when the reconstruction distance is 25cm. Figure 3 (d) is a 3D reconstructed image taken in the left view area at a reconstruction distance of 22cm.

[0013] The figure labels in the above figures are as follows:

[0014] (1) Laser, (2) Beam expander, (3) Collimating lens, (4) Semi-transparent mirror I, (5) Spatial light modulator, (6) Lens I, (7) Filter, (8) Lens II, (9) Polarizer, (10) Semi-transparent mirror II, (11) Liquid crystal polarizing grating, (12) Camera.

[0015] It should be understood that the above figures are only schematic and are not drawn to scale. V. Detailed Implementation Methods

[0016] The following detailed description of an embodiment of a binocular holographic near-eye 3D display system based on liquid crystal polarization grating is provided to further describe the present application. It is necessary to point out here that the following embodiment is only used to further illustrate the present application and cannot be understood as a limitation on the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above description of the present application, which still falls within the protection scope of the present application.

[0017] The system embodiment of the present application is as follows: in the experimental system, the wavelength of the green light source is 532 nm, the spatial light modulator is a reflective pure phase spatial light modulator, the pixel pitch is 6.4 μm, the resolution is 1920×1080, and the phase modulation capability is 0-2π. The focal length of lens I and lens II is 25 cm. The images "airplane, moon, and tree" are used as recorded objects, and the resolutions thereof are all 1920×1080. The hologram is generated based on Python software, and the resolution thereof is 1920×1080. The reconstruction distance of the image "airplane" is set to 25 cm, and the reconstruction distances of the images "moon" and "tree" are set to 22 cm. The real object "H" is set on the same depth plane as the "airplane" as a reference object, and the real object "B" is set on the same depth plane as the "moon" and "tree" as a reference object. The hologram is loaded onto the spatial light modulator, when the collimated light beam irradiates the spatial light modulator, the light beam with object reconstruction information is modulated into linearly polarized light after passing through the polarizer, and then is incident on the liquid crystal polarization grating, and the 3D objects are reconstructed in the left and right viewing zones behind the liquid crystal polarization grating.

[0018] The right viewing zone reconstruction image of the binocular holographic near-eye 3D display system based on liquid crystal polarization grating is shown in FIGS. 5(a) and 5(b). Figure 3 When the camera focuses on the real object "H", the reconstruction image is located at the upper right corner of the pendulum "H", at this time, the reconstruction image "airplane" is clear, and the reconstruction images "moon" and "tree" are blurred. The left viewing zone reconstruction image of the binocular holographic near-eye 3D display system based on liquid crystal polarization grating is shown in FIGS. 6(a) and 6(b). Figure 3 When the camera focuses on the pendulum "B", the reconstruction image is located at the upper left corner of the pendulum "H", the reconstruction images "moon" and "tree" are clear, and the reconstruction image "airplane" is blurred. The experimental results verify that the system realizes the binocular holographic near-eye 3D display effect.

Claims

1. A liquid crystal polarization grating based binocular holographic near-eye 3D display system, characterized in that, The system comprises a laser, a beam expander, a collimating lens, a half-transmission half-reflection mirror I, a spatial light modulator, a 4f filtering system, a half-transmission half-reflection mirror II, a polarizer and a liquid crystal polarization grating, wherein the 4f filtering system comprises a lens I, a filter and a lens II, the laser emitted by the laser is transmitted to the spatial light modulator through the beam expansion of the beam expander and the collimation of the collimating lens, the spatial light modulator is loaded with a hologram of a 3D object generated by a computer in advance, the light beam is diffracted through the spatial light modulator and then enters the 4f filtering system, so that the zero-order light and stray light are eliminated, the light beam from which the zero-order light and stray light are eliminated is modulated into linearly polarized light after passing through the polarizer, the linearly polarized light is reflected by the half-transmission half-reflection mirror II and then is perpendicularly incident on the liquid crystal polarization grating, the left-handed circularly polarized light and the right-handed circularly polarized light contained in the linearly polarized light are deflected in opposite directions along the optical axis after passing through the liquid crystal polarization grating, so that 3D reconstructed images with the same deflection angle are generated in the left and right viewing zones, respectively, the diffraction position of the holographic reconstructed image is set to be the same as the position of the camera, a moving camera is used to simulate two eyes, and the reconstructed images in the left and right viewing zones are recorded, respectively, so that binocular holographic near-eye 3D display effect is obtained. The liquid crystal polarization grating is based on geometric phase control and has dielectric anisotropy, and only two diffraction orders, i.e., +1 order and -1 order, are generated after the laser is incident on the liquid crystal polarization grating, the liquid crystal polarization grating selectively emits +1 order or -1 order diffracted light according to the polarization state of the incident light, when the laser irradiates the liquid crystal polarization grating, the +1 order and -1 order diffracted light deviates from the original incident direction due to geometric phase control, when the linearly polarized light is perpendicularly incident on the liquid crystal polarization grating, the diffraction angle a of the +1 order and -1 order diffracted light satisfies the following equation: wherein Λ and λ g are the period and working wavelength of the liquid crystal polarization grating, respectively, when the left-handed circularly polarized light is normally incident on the liquid crystal polarization grating, the polarization state of the diffracted light is modulated into right-handed circularly polarized light and deviates from the optical axis by an angle of a, when the right-handed circularly polarized light is normally incident on the liquid crystal polarization grating, the polarization state of the diffracted light is modulated into left-handed circularly polarized light and deviates from the optical axis by an angle of -a, since linearly polarized light is regarded as a collection of left-handed and right-handed circularly polarized light, when linearly polarized light is normally incident on the liquid crystal polarization grating, the polarization states of the left-handed and right-handed circularly polarized light therein are changed, respectively, thereby forming +1 order and -1 order diffracted light, respectively, and deflecting to left and right viewing zones by angles of a and -a, respectively. 2.The binocular holographic near-eye 3D display system based on liquid crystal polarization grating of claim 1, wherein, Binocular holographic near-eye 3D display requires that the reconstructed images enter the left and right eyes of the viewer, respectively, and therefore the distance between the two reconstructed images in the left and right viewing zones needs to correspond to the interpupillary distance of the two eyes, and the diffraction angle a and the interpupillary distance d of the two eyes satisfy the following formula: wherein l is the distance between the liquid crystal polarization grating and the human eye, and the diffraction angle is calculated based on the distance between the liquid crystal polarization grating and the human eye and the interpupillary distance of the two eyes, so that the period of the liquid crystal polarization grating is determined, so as to meet the requirement of binocular holographic near-eye 3D display.

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